For more than five years, astronomers have sounded alarms about the effect satellite megaconstellations would have on their observations. The launch in 2019 of the first Starlink satellites, initially bright enough to be seen by the naked eye, led astronomers to spring to action to both raise awareness about the threat and to work with companies like SpaceX to reduce potential interference.
Those efforts have, at a minimum, avoided worst-case scenarios about the impact of megaconstellations. Of particular concern was the effect Starlink and other systems would have on the new Vera C. Rubin Observatory in Chile, scheduled to begin observations later this year. The telescope’s wide field of view and sensitive camera, designed to survey the entire southern sky every three days, caused astronomers to worry its images would be criss-crossed with streaks from satellites, reducing their scientific utility.
For now, Rubin Observatory astronomers say, the problem is manageable.
“It’s merely a nuisance and not catastrophic,” said Yusra AlSayyad, a Rubin astronomer, during a briefing at the 245th Meeting of the American Astronomical Society (AAS) Jan. 16. She estimated that fewer than 1% of pixels on each image will be affected by satellites.
Astronomers are not declaring victory. Instead, while they continue to work on satellite interference issues, they are expanding their work to other topics broadly associated with space sustainability. These issues range from the threat of obtrusive space advertising and reentries that interfere with their observations to the danger of confusing asteroids with flying Teslas.
Reentries and the fake asteroid phenomenon
At the AAS meeting, the largest annual conference for astronomers, the organization announced it had adopted a new resolution opposing the development of what is known as “obtrusive space advertising,” or satellites in orbit displaying advertising images that can be seen from the ground. Just like satellite megaconstellations, astronomers worry such advertising could interfere with their observations.
That concern is, for now, largely a theoretical one. In the United States, federal law has banned obtrusive space advertising for decades, but John Barentine of Dark Sky Consulting, a member of the AAS’s Committee for the Protection of Astronomy and the Space Environment (COMPASSE), said the AAS is worried that other nations, like Russia, might allow it.
“There is reason to believe that this activity will be pursued globally,” he said at a briefing during the AAS meeting. “The lure of it is so great that I can’t imagine that no one will try.” He said the AAS is urging other nations to adopt bans on space advertising like the U.S. has done.
While interference from space advertising remains hypothetical, other phenomena are happening now. One is so-called “ionospheric holes” created when exhaust from upper stages performing deorbiting burns interacts with the ionosphere, creating a bright red glow in the night sky that can linger for a half-hour.
“They’re one of the wildest things you can see in the night sky,” said Stephen Hummel of McDonald Observatory at the AAS meeting. “When I saw my first ionospheric hole, I thought, ‘OK, aliens are real.’”
Officials at McDonald Observatory, located in West Texas, regularly see ionospheric holes from Falcon 9 launches from Florida, with the upper stage performing a deorbit burn in view of the observatory after nearly one orbit to reenter over the South Atlantic Ocean. “It can be pretty impactful for anything in that region of the sky,” he said of the effect they can have on astronomy.
Astronomers are, for now, not seeking any specific action to address ionospheric holes and instead are working to better understand them. “They are quite difficult to predict accurately,” Hummel said. “We look forward to collaborating with others to try to predict these events.”
It’s not just reentering rockets that worry astronomers. Last September, the AAS published a statement about reentries of satellites, citing concerns about how the increasing number of satellites could affect the atmosphere when those spacecraft reenter at the end of their lives.
Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who also tracks spaceflight activities, noted in a session at the conference that up to 10% of stratospheric aerosols are now “little blobs of melted satellites” and that metal from satellites in the upper atmosphere now exceeds what is deposited naturally from meteors.
More recently, the AAS has focused on how the environmental impacts of satellite reentries could hurt the work of astronomers. “Pollution from reentries could potentially increase the opacity of Earth’s atmosphere,” it noted in its statement, affecting ground-based observations, “and could induce an airglow that increases the night sky brightness, limiting our ability to study faint astronomical objects.”
Astronomers’ interest in space sustainability goes beyond the atmosphere and satellites in Earth orbit. The AAS published another statement last year calling for “transparency” in operations in cislunar space and beyond. It asked governments and companies to share more information on spacecraft traveling beyond Earth orbit.
That sharing of information, the organization argues, is needed for safe space operations. It can also help astronomers avoid confusing spacecraft with objects like asteroids. “We have multiple cases of newly discovered asteroids turning out not to be asteroids after all,” McDowell said. That included a recent case where, he recalled, “we had to retire one from the catalog because it was actually Elon (Musk)’s Tesla” from the first Falcon Heavy launch.
Struggling to take action
However, turning those concerns about satellite interference or other space sustainability issues into action has been difficult. A lack of information, funding and authority have stymied efforts by astronomers to convince government agencies to act.
“I get asked a lot as a policy analyst, why not just pass a law that says what the satellite brightness should be?” said Lindsay DeMarchi, a senior policy analyst at The Aerospace Corporation, a nonprofit corporation performing technical and policy assessments on space topics.
The problem, she said, is that different telescopes have different sensitivities, while predicting the brightness of a satellite as seen from the ground can be difficult.
Moreover, while companies like SpaceX have made strides in reducing the brightness of their satellites, they have run into problems meeting recommended brightnesses set by astronomers.
One proposal to improve that effort was legislation introduced last year by Sens. John Hickenlooper (D-Colo.) and Mike Crapo (R-Idaho) to create a center of excellence, overseen by the National Institute of Standards and Technology, to study ways satellite developers can mitigate interference.
“You can think of the center of excellence as kind of like a university or nonprofit with its sights set on material advances towards dark and quiet skies,” she said, leveraging existing facilities for testing around the country. The bill did not pass but may be reintroduced in some form this year.
Similarly, while there is interest among astronomers and other scientists to better understand how satellite reentries are affecting the atmosphere, there is little funding for research on the topic, and no agreement about who should be supporting that research.
“There needs to be a lot more research. We really don’t understand this problem very well at all,” said Marlon Sorge, executive director of Aerospace Corporation’s Center for Orbital and Reentry Debris Studies, during a briefing in December about Aerospace’s annual Space Safety Compendium report. He stopped short, though, of recommending how much funding should go toward reentry research or which agencies should fund it.
Representatives of government agencies said it was difficult to regulate space sustainability concerns raised by astronomers under current laws, citing the Supreme Court’s ruling last year that struck down the legal concept known as “Chevron deference” that gave agencies wider latitude to regulate.
“I do think the ability of regulators to interpret things like dark and quiet skies into broader grants of authority that people hadn’t anticipated when the laws were passed will be increasingly called into question,” said Gabriel Swiney, director of the Office of Space Commerce’s policy, advocacy and international division, at the AAS meeting.
He spoke on a panel with Steph Earle of the FAA’s Office of Commercial Space Transportation, who offered a similar view. “A lot of the things that were brought up today don’t fit” into areas the FAA can consider when reviewing a launch license application, he said. “If legislation comes forward, then I can do something in those areas.”
For now, the most effective path for near-term action on space sustainability is astronomers working directly with satellite and launch companies. Such cooperation has been ongoing in reducing the brightness of satellites and is now extending into other areas, such as radiofrequency interference. The National Science Foundation (NSF) announced an agreement with SpaceX last August to cooperate on approaches to reduce interference between Starlink and NSF-funded radio telescopes.
“There used to be a real hatred between radio astronomy and satellite operators,” recalled Jennifer Manner, a former satellite industry executive who is now senior adviser for space and satellite policy at the National Telecommunications and Information Administration. There has been a “sea change” in that relationship more recently, she said. “There’s real respect and willingness to get things done. That’s something that’s really important.”
This article first appeared in the February 2025 issue of SpaceNews Magazine with the title “Clearing the Skies”
